Chitin, colloidal chitin and water-soluble chitosan were hydrolyzed by crude enzyme solution produce by Bacillus amyloliquefaciens V656. The hydrolysates with 12 h hydrolysis contained optimal (GlcNAc)(6) and showed higher antitumor activity. Among those chitinous materials, the most effective one was the hydrolysates of water-soluble chitosan, which inhibited the growth of CT26 cells and reduced the survival rate to 34% in 1 day. Since the hydrolysate of water-soluble chitosan contained the optimal hexamer/(GlcNAc)(6) at 12 h, it is conjectured that the antitumor activity should be related to (GlcNAc)(6). This conjecture was further affirmed by experiment with pure (GlcNAc)(6). However, This phenomenon might be due to the synergistic effect of the oligomers (GlcNAc)(n), n = 1-6 in the hydrolysates. The antitumor effect of the chitinous hydrolysates is worth further investigation. The aim of this study was to investigate the induced apoptosis in CT26 cells by the hydrolysates of chitinous materials. It was found that the hydrolysates (A, B and C) inhibited the survival of CT26 cells in a concentration- and time-dependent manner. The hydrolysates induced characteristic DNA fragmentation of the CT26 cells. These results suggested that the hydrolysates from chitinous materials are potent apoptosis-inducing agents for CT26 cells. (c) 2006 Elsevier Ltd. All rights reserved.